On a daily basis, vast quantities of water are removed from rivers, lakes, and streams for industrial and commercial uses. For such uses, water conduits may be required to conduct large amounts of water on demand. In particular, the fire protection piping systems of power plants, locks, dams, and other related facilities may be required to conduct large amounts of water on demand when there is an emergency.
The water sources for many of these on-demand water conduits support an abundance of biological life forms. Some of the biological life forms cannot be removed before the water is demanded for industrial or commercial use. While some of these biological life forms may not adversely affect on-demand water systems, macrofoulers such as zebra mussels have had a severe impact.
An on-demand water conduit may be idle when no demand exists for a flow of water. For instance, the intake water conduits of fire protection piping systems may be idle when there is no emergency. Consequently, on-demand water conduits are particularly susceptible to infestation by macrofouling organisms such as zebra mussels when there is no demand for a flow of water.
Infestation of on-demand water conduits by macrofouling organisms such as zebra mussels is a serious and growing problem for two main reasons. Such macrofouling organisms diminish the water carrying capacity of an on-demand water conduit by reducing the effective bore and increasing the roughness of the conduit. In addition, such macrofouling organisms may set up local differences in the state of oxidation on the inner surface of a steel or cast-iron on-demand water conduit which may cause electro-corrosion. These consequences of macrofouling organisms are responsible for much waste in on-demand water systems including increased pumping costs, loss of water carrying capacity, and increased costs for the cleaning, maintenance, and replacement of fouled conduits.
Macrofoulers include any oxygen-dependent organism, sessile or non-sessile, whose presence in a body of water fouls the condition of a structure in the body of water, such as a conduit. The three most common macrofouling organisms in the United States are currently the zebra mussel, the quagga mussel, and the asiatic clam. All of these organisms are dependent on dissolved oxygen for respiration and are, thus, amenable to control by the proposed invention. Other species that are known macrofouling organisms amenable to control by the present invention are Mytilopsis sallei (found in the Gulf of Mexico and Brazil), Musculista senhousia (found in China, Siberia, and adjacent areas), Limnopema fortunei (found in China's fresh waters), and Modiolus striatulus (found in the intake of a potable water system in India). The preceding list is not an exhaustive list of macrofouling organisms amenable to control by the present invention. The transport of organisms between bodies of water and the evolution of new species results in continuous supply of new macrofouling organisms.
Zebra mussels, in particular, attach themselves to water conduits by up to 200 tough threads of a dry horny material called the byssus. Zebra mussels also use these byssal threads to attach themselves to other zebra mussels. Consequently, zebra mussels may form layers more than one inch thick on the interior of water conduits, or they may even form clusters in open water.
Zebra mussels were unknown in the Great Lakes until 1988 when substantial infestations were discovered in southeastern Lake St. Clair. Presumably, the zebra mussels were introduced by ballast water discharged by the tanks of an international shipping boat in 1986. Zebra mussels have since spread throughout Lake Erie with phenomenal speed, and their presence in Lake Michigan near Green Bay, Wis. and Gary, Ind. imply that it is only a matter of time before all of the Great Lakes, the Mississippi River, and the Ohio River are effected. With time, the problem may even extend to every body of surface water in North America. As a result, a wide variety of methods have since been used in an attempt to control infestation by zebra mussels.
Scraping has been used to remove existing growth of zebra mussels from mains, tanks, and conduits. This method is slow and expensive, and it cannot remove every zebra mussel from the mains, tanks, or conduits. Moreover, the mains, tanks, or conduits cannot be in service during the scraping treatment.
High pressure water has also been used for removing zebra mussels from walls, trash racks, and other equipment. An example of such a mechanical cleaning device is taught in U.S. Pat. No. 5,069,722. For this treatment, a suction pump is normally attached to a mechanical scrapper which can be used to dislodge and vacuum the zebra mussels out of an area. This method, of course, requires the operation and maintenance of the equipment by a work force. In addition, this method may not work for water conduits that have a small diameter.
Another method which has been used for controlling zebra mussels is the application of toxic and non-toxic coated materials which can either prevent zebra mussel settlement or cause very weak byssal attachment. These materials include silicone and epoxy compounds, copper-based paints, and thermal metallic sprays. Such materials can be used on structures that are difficult to clean, or if there are anticipated difficulties with removal and disposal of large numbers of zebra mussels. However, some of the drawbacks of the use of such materials include the expense of the materials, the expense of applying the materials, and the possibility that the materials may render the water inappropriate for some end uses.
Many oxidizing and non-oxidizing chemical control agents have also been used to reduce or eliminate zebra mussels. Chlorine is a commonly used control agent in Europe, the U.S., and Canada, and it can be used in pipes or ducts that contain pressure sensing or other equipment. Continuous exposure to chlorine at 0.5 mg/L will kill zebra mussels in 14 to 21 days. Chlorine, however, is toxic to humans and animals, and it produces undesirable, even carcinogenic, chlorinated organic compounds in the water. Moreover, chlorine corrodes the operating equipment.
A wide variety of other chemical agents have been used in an attempt to control infestation by zebra mussels. These include the use of a nitrostyrene compound and an alkyl thiocyanate compound as taught in U.S. Pat. No. 4,579,665; the use of a water-soluble alkyl guanidine salt as taught in U.S. Pat. No. 4,816,163; the use of a water-soluble quaternary ammonium salt, such as those taught in U.S. Pat. No. 4,857,209; the use of an alkylthioalkylamine or acid addition salt thereof, such as that taught in U.S. Pat. No. 4,970,239; the use of a water-soluble dialkyl diallyl quaternary ammonium polymer (polyquat), such as that taught in U.S. Pat. No. 5,015,395; the use of an effective amount of ozone, such as that taught in U.S. Pat. No. 5,040,487; the use of didecyl dimethyl ammonium halide such as taught in U.S. Pat. No. 5,062,967; the use of a combination of a chlorine solution and a bromide salt capable of releasing bromide ions, such as taught in U.S. Pat. No. 5,141,754; and the use of a glutaraldehyde, such as taught in U.S. Pat. No. 5,160,047.
Chemical methods such as those described above have the obvious disadvantages of requiring the purchase of expensive chemicals as well as the need to use skilled operators in their application. Such chemical methods also have a toxic and polluting effect that may be inappropriate for the end use. Furthermore, such chemical methods cannot be effectively used in an on-demand water conduit.
On the other hand, thermal processes have been demonstrated to be a successful control technology. The post veliger and settling larvae of zebra mussels are the most sensitive to temperature shock and anoxia. It has been shown that zebra mussels acclimated to a water temperature between 5 degrees Celsius and 15 degrees Celsius would go into thermal shock when the water temperature reached approximately 30 degrees Celsius, and it has been shown that zebra mussels acclimated to a water temperature of 25 degrees Celsius would go into thermal shock when the water temperature reached approximately 35 degrees Celsius. Thermal processes, however, may have ecological impacts on other aquatic life.
Dissolved oxygen is essential for zebra mussels especially at the stage of their settling on hard substrata. As taught in U.S. Pat. No. 5,578,116, oxygen deprivation is a control technique for removing zebra mussels from water conduits. The present invention is an improvement over U.S. Pat. No. 5,578,116, and the disclosure of U.S. Pat. No. 5,578,116 is hereby incorporated by reference. U.S. Pat. No. 5,578,116 provides a mechanical method for controlling zebra mussels which may be applied to a flow of water. Consequently, the method of U.S. Pat. No. 5,578,116 is not readily applicable to an on-demand water conduit.
Accordingly, it is an object of the present invention to provide a method and apparatus for controlling macrofoulers and the larvae thereof in an on-demand water conduit, such as an emergency water conduit and its associated intake structures. It is also desirable to be able to develop a method and apparatus which can be implemented without the use of skilled operators or workmen. In view of the present disclosure and the practice of the present invention, other advantages of the present invention may become apparent.